Synchronization of automotive sensors using communication-link TDM timing

ABSTRACT

An automotive communication system includes multiple communication devices and a processor. The communication devices are configured to be installed in a vehicle and to communicate with one another over point-to-point Ethernet links. In each Ethernet link, a first communication device serves as a link master that is configured to set a clock signal for the link, and a second communication device serves as a slave that is configured to synchronize to the clock signal set by the first communication device. The communication devices are configured to receive data from sensors and to transmit the data over the Ethernet links. The processor is configured to receive the data from the communication devices over the Ethernet links, to synchronize the data originating from the multiple sensors to a common time-base based on link-specific clock-signal synchronization achieved on each of the links by each link master, and to process the synchronized data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication 62/816,765, filed Mar. 11, 2019, whose disclosure isincorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication systems, andparticularly to full-duplex communication and network synchronizationusing Ethernet™ links.

BACKGROUND

Various applications, such as automotive in-car communication systems,certain industrial communication systems and smart-home systems, requirecommunication at high data rates over relatively small distances.Several types of protocols and communication media have been proposedfor such applications. For example, Ethernet communication overtwisted-pair copper wire media is specified in “IEEE 802.3bw-2015—IEEEStandard for Ethernet Amendment 1: Physical Layer Specifications andManagement Parameters for 100 Mb/s Operation over a Single BalancedTwisted Pair Cable (100BASE-T1),” March, 2015.

The description above is presented as a general overview of related artin this field and should not be construed as an admission that any ofthe information it contains constitutes prior art against the presentpatent application.

SUMMARY

An embodiment that is described herein provides an automotivecommunication system including multiple communication devices and aprocessor. The communication devices are configured to be installed in avehicle and to communicate with one another over a plurality ofpoint-to-point Ethernet links. In each link among the Ethernet links, arespective first communication device serves as a link master that isconfigured to set a clock signal for the link, and a respective secondcommunication device serves as a slave that is configured to synchronizeto the clock signal set by the first communication device. Thecommunication devices are configured to receive data from multiplesensors and to transmit the data over the Ethernet links. The processoris configured to receive the data from the communication devices overthe Ethernet links, to synchronize the data originating from themultiple sensors to a common time-base based on link-specificclock-signal synchronization achieved on each of the links by each linkmaster, and to process the synchronized data.

In some embodiments, in each link, the respective link master and therespective slave are configured to communicate over the link in atime-division multiplexing (TDM) protocol including master-to-slavetransmission periods and slave-to-master transmission periods, whilemaintaining synchronization to the clock signal of the link master bothduring the master-to-slave transmission periods and during theslave-to-master transmission periods.

In an example embodiment, in each link, the respective slave isconfigured to: (i) during the master-to-slave transmission periods, locka local oscillator of the slave on the clock signal of the link master,and (ii) during the slave-to-master transmission periods, transmit datausing the local oscillator that was locked on the clock signal of thelink master during the master-to-slave transmission periods.

In a disclosed embodiment, the processor is configured to construct athree-dimensional image from the data that originated from the multiplesensors, received over the multiple Ethernet links and synchronized tothe common time-base. In another embodiment, the processor is configuredto receive the data from at least two sensors over at least two separateEthernet links. In yet another embodiment, the sensors include imagesensors configured to acquire images of a scene, and the processor isconfigured to construct a three-dimensional model of at least part ofthe scene from the images.

There is additionally provided, in accordance with an embodiment that isdescribed herein, a method for data processing in an automotivecommunication system. The method includes receiving data from multiplesensors in a plurality of communication devices installed in a vehicle.The data is communicated between the communication devices over aplurality of point-to-point Ethernet links to a processor, including, ineach link among the Ethernet links, assigning a respective firstcommunication device to serve as a link master that sets a clock signalfor the link, and assigning a respective second communication device toserve as a slave that synchronizes to the clock signal set by the firstcommunication device. In the processor, the data is received from thecommunication devices over the Ethernet links, the data originating fromthe multiple sensors is synchronized to a common time-base based onlink-specific clock-signal synchronization achieved on each of the linksby each link master, and the synchronized data is processed.

There is also provided, in accordance with an embodiment that isdescribed herein, an industrial communication system including multiplecommunication devices and a processor. The communication devices areconfigured to communicate with one another over a plurality ofpoint-to-point Ethernet links. In each link among the Ethernet links, arespective first communication device serves as a link master that isconfigured to set a clock signal for the link, and a respective secondcommunication device serves as a slave that is configured to synchronizeto the clock signal set by the first communication device. Thecommunication devices are configured to receive data from multiplesensors and to transmit the data over the Ethernet links. The processoris configured to receive the data from the communication devices overthe Ethernet links, to synchronize the data originating from themultiple sensors to a common time-base based on link-specificclock-signal synchronization achieved on each of the links by each linkmaster, and to process the synchronized data.

There is further provided, in accordance with an embodiment that isdescribed herein, a method for data processing in an industrialcommunication system. The method includes receiving data from multiplesensors in a plurality of communication devices. The data iscommunicated between the communication devices over a plurality ofpoint-to-point Ethernet links to a processor, including, in each linkamong the Ethernet links, assigning a respective first communicationdevice to serve as a link master that sets a clock signal for the link,and assigning a respective second communication device to serve as aslave that synchronizes to the clock signal set by the firstcommunication device. In the processor, the data is received from thecommunication devices over the Ethernet links, the data originating fromthe multiple sensors is synchronized to a common time-base based onlink-specific clock-signal synchronization achieved on each of the linksby each link master, and the synchronized data is processed.

The present disclosure will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram that schematically illustrates an automotivecommunication system, in accordance with an embodiment that is describedherein;

FIG. 2 is a flow chart that schematically illustrates a method forTime-Division Multiplexing (TDM) communication over an Ethernet link inthe system of FIG. 1, in accordance with an embodiment that is describedherein; and

FIG. 3 is a flow chart that schematically illustrates a method forgenerating a three-dimensional model from automotive sensor images inthe system of FIG. 1, in accordance with an embodiment that is describedherein.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments that are described herein provide improved methods andsystems for communication over Ethernet™ links. The embodimentsdescribed herein are described in the context of automotiveapplications, e.g., systems that collect data from sensors within avehicle. This choice, however, is made solely for the sake of clarity.The disclosed techniques are equally applicable in other applications,for example in industrial and/or smart-home networks.

In some embodiments, an automotive communication system comprisesmultiple communication devices, also referred to as “PHY devices.” Thecommunication devices are configured to be installed in a vehicle and tocommunicate with one another over a plurality of point-to-point Ethernetlinks, e.g., twisted-pair links. At least some of the communicationdevices are connected to sensors fitted in the vehicle, e.g., cameras,radar sensors and the like. By communicating over the Ethernet links,the communication devices transfer data collected by the sensors to acentral processor, and transfer control information from the processorto the sensors.

Unlike conventional Ethernet operation, however, in the disclosedembodiments each pair of communication devices connected by an Ethernetlink communicate with one another in a Time-Division Multiplexing (TDM)protocol.

In an embodiment, in each link among the Ethernet links, onecommunication device serves as a link master, and the othercommunication device serves as a slave. The link master is configured toset (i) a clock signal for the link and (ii) timing of master-to-slavetransmission periods and slave-to-master transmission periods in the TDMprotocol over the link. The slave is configured to synchronize to theclock signal and to the TDM timing set by the link master. In settingthe master-to-slave and slave-to-master transmission periods, in someembodiments the link master also sets an adjustable duty-cycle betweenthe master-to-slave and slave-to-master link directions.

Although the disclosed TDM operation increases the instantaneous datarate over the Ethernet link, the fact that transmission isunidirectional at any given time simplifies the communication devicesconsiderably. For example, conventional full-duplex operation over atwisted-pair link requires the use of hybrid combiners and complex echocancellation circuitry in the Ethernet PHY devices. The disclosed TDMoperation obviates the need for these elements, thereby reducing thesize, cost and power consumption of the communication devices.

In some embodiments, the central processor receives the data produced bythe multiple sensors and transferred by the multiple communicationdevices over the multiple Ethernet links. The processor is configured tosynchronize the data originating from the various sensors to a commontime-base, based on the link-specific synchronizations set on the linksby the respective link master, and to process the synchronized data.

In one example embodiment, the sensors comprise image sensors, e.g.,video cameras, which acquire two-dimensional (2-D) images of a scene inthe vicinity of the vehicle. By synchronizing images from multiple imagesensors to a common time-base, the processor is able to generate athree-dimensional (3-D) image or model of at least part of the scene.3-D imaging or modeling of this sort provides valuable information suchas distances to nearby objects.

FIG. 1 is a block diagram that schematically illustrates an automotivecommunication system 20, in accordance with an embodiment that isdescribed herein. System 20 is installed in a vehicle 24, and comprisesmultiple sensors 28, multiple communication devices 32 that communicateover point-to-point Ethernet links 36, and a central processor 40.

In various embodiments, sensors 28 may comprise any suitable types ofsensors. Several non-limiting examples of sensors comprise videocameras, velocity sensors, accelerometers, audio sensors, infra-redsensors, radar sensors, lidar sensors, ultrasonic sensors, rangefindersor other proximity sensors, and the like.

Communication devices 32 typically operate at least partially inaccordance with one or more of the IEEE 802.3 Ethernet standards, e.g.,the IEEE 802.3bw-2015, cited above. Since the techniques describedherein pertain mainly to the physical layer, communication devices 32are also referred to herein as “PHY devices.” Nevertheless, in someembodiments communication devices 32 perform Medium Access Control (MAC)functions as well.

Depending on the applicable Ethernet standard, links 36 may comprise anysuitable physical medium. In the embodiments described herein, althoughnot necessarily, each link 36 comprises a single pair of wires, i.e., asingle twisted-pair link. In alternative embodiments, links 36 maycomprise single-ended wire links, not necessarily Ethernet compliant.

As seen in the figure, each link 36 is used for point-to-pointcommunication between two communication devices 32. Communicationdevices 32 and links 36 are connected in a suitable topology so as tocommunicate with processor 40. In the example of FIG. 1, two of links 36(at the top of the figure) are connected back-to-back, in which casedata from a sensor 28 traverses two links 36 until reaching processor40. A back-to-back configuration is useful, for example, when the twolinks 36 are fitted in two separate parts of vehicle 24. A third link 36(at the bottom of the figure) connects the communication device thatserves a sensor 28 directly to the communication device that servesprocessor 40. In various embodiments, one or more of communicationdevices 32 may be connected to sensors 28, and one or more othercommunication devices 32 may not be connected to sensors. In the presentexample, processor 40 is connected to a dedicated communication device32. In other embodiments, the same communication device 32 may serveboth processor 40 and a sensor 28. By the same token, a communicationdevice may serve more than a single sensor 28. Further alternatively,any other suitable interconnection topology can be used for connectingsensors 28 and processor 40 using communication devices 32 and Ethernetlinks 36.

An inset at the bottom-left of FIG. 1 shows an example of twocommunication devices 32 that communicate over an Ethernet link 36. Insome embodiments, in any pair of communication devices 32 thatcommunicate over a respective link 36, one of the communication devicesserves as a link master and the other serves as a slave. In the presentexample the link master is labeled 32A and the slave is labeled 32B.

On a given link 36, the master and the slave communicate in accordancewith a Time-Division Multiplexing (TDM) protocol, which comprisesinterleaved master-to-slave transmission periods and slave-to-mastertransmission periods. During the master-to-slave transmission periods,the master transmits data over link 36 and the slave receives the data.During the slave-to-master transmission periods, the slave transmitsdata over link 36 and the master receives the data.

Since TDM means that only one communication device transmits at anygiven time, the instantaneous data rate has to be increased. Forexample, to support a throughput of 25 Gbps per direction, theinstantaneous data rate (bandwidth) over link 36 should be at least 50Gbps (and typically slightly higher, e.g., 52 Gbps, to allow foroverhead).

In an example embodiment, the overall TDM period (i.e., onemaster-to-slave transmission period plus one slave-to-mastertransmission period) is on the order of one second. Alternatively, anyother suitable period can be used.

In an example embodiment, the TDM duty-cycle (the ratio between theduration of the master-to-slave transmission period and the duration ofthe slave-to-master transmission period) is 0.5 (i.e., 50%/50%). Inother embodiments, any other suitable duty-cycle can be used, e.g., 0.9(90%/10%) or 0.1 (10%/90%). In some embodiments, the TDM duty-cycle isconfigurable and is set by the link master. The TDM duty-cycle can beset to different values for different links 36 (i.e., for differentmaster-slave pairs).

An inset on the right-hand side of FIG. 1 shows the internal structureof communication device 32, in an embodiment. Communication device 32comprises suitable interfaces for connecting to a sensor 28 (e.g., forreceiving data acquired by the sensor and for transmitting controlinformation to the sensor) and to an Ethernet link 36 (e.g., fortransmitting the data received from the sensor and for receiving controlinformation for the sensor).

In an embodiment, communication device 32 comprises transmission PHY (TXPHY) circuitry 42 that carries out various transmission tasks of thecommunication device, reception PHY (RX PHY) circuitry 44 that carriesout various reception tasks of the communication device, a controller 46that manages the communication device, and clock circuitry 48. In anembodiment, clock circuitry 48 comprises a clock oscillator and aPhase-Locked Loop (PLL).

In the present embodiment, communication device 32 is configurable toserve either as a link master or as a slave. The assumption is that, foreach link 36, one communication device is pre-configured to serve as alink master and the other communication device is pre-configured toserve as a slave. This configuration can be performed, for example, byprocessor 40 on system initialization.

Controller 46 and clock circuitry 48 operate differently, depending onwhether the communication device serves as a link master or as a slave.In a communication device 32 that operates as a link master, controller46 typically sets the clock signal and the TDM protocol for the link.This setting comprises, for example, the TDM duty-cycle and thestart/end times of the master-to-slave and slave-to-master transmissionperiods. When operating as a link master, the clock oscillator in clockcircuitry 48 generates a clock signal for the link.

In a communication device 32 that operates as a slave, the communicationdevice typically tracks and synchronizes to the clock signal and to theTDM protocol set by the link master. In a slave, RX PHY 44 receives thesignal transmitted by the link master, and extracts the clock signalfrom the received signal. The PLL in clock circuitry 48 locks on theextracted clock signal, thereby synchronizing the local clock oscillatorof the slave to the clock signal of the link master. In addition,controller 46 synchronizes to the TDM timing of the received signal,e.g., to the start and end times of the master-to-slave andslave-to-master transmission periods. The clock and/or timingsynchronization between a link master and a slave is referred to hereinas “link-specific synchronization” since it is specific to each link 36,and is typically performed separately by each master-slave pair.

The configurations of system 20 and its elements, such the internalstructure of communication devices 32, as shown in FIG. 1, are exampleconfigurations that are depicted solely for the sake of clarity. Inalternative embodiments, any other suitable configurations can be used.Elements that are not mandatory for understanding of the disclosedtechniques have been omitted from the figure for the sake of clarity.

The different elements of system 20 and its various components, suchprocessor 40 and communication devices 32, may be implemented usingdedicated hardware or firmware, such as using hard-wired or programmablelogic, e.g., in an Application-Specific Integrated Circuit (ASIC) orField-Programmable Gate Array (FPGA). Additionally or alternatively,some functions, e.g., functions of processor 40 and/or of controllers46, may be implemented in software and/or using a combination ofhardware and software elements.

In some embodiments, processor 40 and/or controllers 46 compriseprogrammable processors, which are programmed in software to carry outthe functions described herein. The software may be downloaded to any ofthe processors in electronic form, over a network, for example, or itmay, alternatively or additionally, be provided and/or stored onnon-transitory tangible media, such as magnetic, optical, or electronicmemory.

FIG. 2 is a flow chart that schematically illustrates a method forTime-Division Multiplexing (TDM) communication over an examplepoint-to-point Ethernet link 36 in system 20 of FIG. 1 above, inaccordance with an embodiment that is described herein. As seen in thefigure, operation of the link can be viewed as a training stage,followed by an alternating sequence of master-to-slave transmissionperiods and slave-to-master transmission periods.

The method begins with the communication device 32 that serves as thelink master transmitting a training sequence to the communication device32 that serves as the slave, over link 36, at a training transmissionoperation 50. As part of the training sequence, or as separatesignaling, the master notifies the slave of the TDM timing, e.g., thedurations and start/end times of the master-to-slave and slave-to-mastertransmission periods. The TDM timing is also referred to as a “TX/RXpattern.” At a training reception operation 54, the slave receives thetraining sequence from the master, acquires the master's clock signal bylocking the PLL, and synchronizes to the TDM timing (TX/RX pattern) setby the master. At this stage, initial synchronization has beenestablished, and the master and slave are ready to begin normalbidirectional communication.

At a master transmission operation 58, the master transmits data to theslave during a master-to-slave transmission period. At a slave receptionoperation 62, the slave retains its PLL locked on the master's clocksignal, and receives the data sent from the master. At the end of themaster-to-slave transmission period, the slave's local clock oscillatoris locked on the clock frequency of the master's clock signal.

At this stage, in accordance with the TDM protocol, controllers 46 ofthe master and of the slave switch from master-to-slave transmission toslave-to-master transmission.

At a hold-over operation 66, the slave begins to operate in a hold-overmode. In this mode, the slave generates a clock signal from its localclock oscillator, but in a free-running manner that is not locked on anyreceived signal. At a slave transmission operation 70, the slavetransmits data to the master. For this transmission (and for the entireduration of the slave-to-master transmission period) the slave relies onthe accuracy of its local clock oscillator, which was locked on themaster's clock signal during the preceding master-to-slave transmissionperiod.

At the end of the slave-to-master transmission period, controllers 46 ofthe master and of the slave switch from slave-to-master transmission tomaster-to-slave transmission. The method then loops back to mastertransmission operation 58 above.

With regard to time synchronization, the description up to this pointreferred mainly to link-specific synchronization, i.e., synchronizationbetween the master and the slave over a particular Ethernet link 36. Insome embodiments, central processor 40 of system 20 is configured tosynchronize the data it receives from the various sensors 28 over thevarious Ethernet links 36 to a common time-base. Central processor 40performs this global synchronization based on the link-specificsynchronizations set on the various links 36 by the respective linkmasters.

Synchronizing the data of different sensors to a common time-base isimportant in various use-cases in the automotive environment. In oneexample embodiment, two or more of sensors 28 comprise image sensors,e.g., video cameras, which acquire 2-D images of the scene in thevicinity of vehicle 24. Processor 40 is configured to construct a 3-Dimage or model of at least part of the scene from the 2-D imagesprovided by the image sensors. In order to construct a 3-D model orimage, it is necessary that the acquisition times of the images fromdifferent image sensors be synchronized to a common time-base.

FIG. 3 is a flow chart that schematically illustrates a method forgenerating a three-dimensional model from images acquired by imagesensors in system 20, in accordance with an embodiment that is describedherein. The method begins with sensors 28 (image sensors in the presentexample) acquiring 2-D images, at an acquisition operation 80. At asensor transmission operation 84, sensors 28 send the images tocommunication devices 32.

At a communication operation 88, communication devices 32 send theimages over Ethernet links 36, finally reaching central processor 40.Communication over links 36 is performed using TDM, with the slave ofeach link being synchronized to the respective link master, as describedabove.

At a global synchronization operation 92, processor 40 synchronizes theimages acquired by the various image sensors 28 to a common time-base,based on the link-specific synchronizations on the various links 36.

At a model construction operation 96, processor 40 uses theglobally-synchronized images to construct a 3-D model of at least partof the vicinity of vehicle 24.

The method flows of FIGS. 2 and 3 are example flows that are depictedsolely for the sake of clarity. In alternative embodiments, any othersuitable flows can be used. For example, in alternative embodimentsprocessor 40 is configured to construct a 3-D model or image of thevicinity of vehicle 24 by fusing data from other types of sensors, notnecessarily images. Such sensors may comprise, for example, proximitysensors, radar sensors or lidar sensors, or a mix of multiple types ofsensors. In such embodiments, too, it is important to synchronize thedata acquired by the various sensors to a common time-base.

Although the embodiments described herein mainly address automotivenetwork communication systems, the methods and systems described hereincan also be used in other applications, such as in industrial networkcommunication systems that use Ethernet links to collect data fromsensors and/or control various devices in an industrial environment, andin smart-home systems that collect data from, and control, home sensorsand appliances.

It is noted that the embodiments described above are cited by way ofexample, and that the present invention is not limited to what has beenparticularly shown and described hereinabove. Rather, the scope of thepresent invention includes both combinations and sub-combinations of thevarious features described hereinabove, as well as variations andmodifications thereof which would occur to persons skilled in the artupon reading the foregoing description and which are not disclosed inthe prior art. Documents incorporated by reference in the present patentapplication are to be considered an integral part of the applicationexcept that to the extent any terms are defined in these incorporateddocuments in a manner that conflicts with the definitions madeexplicitly or implicitly in the present specification, only thedefinitions in the present specification should be considered.

The invention claimed is:
 1. An automotive communication system,comprising: multiple communication devices, configured to be installedin a vehicle and to communicate with one another over a plurality offull-duplex point-to-point Ethernet links, wherein in each link amongthe Ethernet links, a respective first communication device serves as alink-specific master that is configured to set a link-specific clocksignal for the link, and a respective second communication device servesas a link-specific slave that is configured to synchronize to thelink-specific clock signal set by the first communication device,wherein in a given full-duplex point-to-point Ethernet link therespective link-specific master and the respective link-specific slaveare configured to communicate in a time-division multiplexing (TDM)protocol comprising unidirectional master-to-slave transmission periodsand unidirectional slave-to-master transmission periods, and wherein thecommunication devices are configured to receive data from multiplesensors and to transmit the data over the Ethernet links.
 2. Theautomotive communication system according to claim 1, wherein in thegiven link, the respective link-specific slave is configured to: duringthe master-to-slave transmission periods, lock a local oscillator of thelink-specific slave on the link-specific clock signal of thelink-specific master; and during the slave-to-master transmissionperiods, transmit data using the local oscillator that was locked on thelink-specific clock signal of the link-specific master during themaster-to-slave transmission periods.
 3. The automotive communicationsystem according to claim 1, further comprising a processor configuredto receive the data from the communication devices over the Ethernetlinks, to synchronize the data originating from the multiple sensors toa common time-base based on link-specific clock-signal synchronizationachieved on each of the links by each link-specific master, and toprocess the synchronized data.
 4. The automotive communication systemaccording to claim 3, wherein the processor is configured to construct athree-dimensional image from the data that originated from the multiplesensors, received over the multiple Ethernet links and synchronized tothe common time-base.
 5. The automotive communication system accordingto claim 3, wherein the processor is configured to receive the data fromat least two sensors over at least two separate Ethernet links.
 6. Theautomotive communication system according to claim 3, wherein thesensors comprise image sensors configured to acquire images of a scene,and wherein the processor is configured to construct a three-dimensionalmodel of at least part of the scene from the images.
 7. A method fordata processing in an automotive communication system, the methodcomprising: receiving data from multiple sensors in a plurality ofcommunication devices installed in a vehicle; and communicating the databetween the communication devices over a plurality of full-duplexpoint-to-point Ethernet links, including, in each link among theEthernet links, assigning a respective first communication device toserve as a link-specific master that sets a link-specific clock signalfor the link, and assigning a respective second communication device toserve as a link-specific slave that synchronizes to the link-specificclock signal set by the first communication device, whereincommunicating the data comprises, in a given full-duplex point-to-pointEthernet link, communicating between the respective link-specific masterand the respective link-specific slave in a time-division multiplexing(TDM) protocol comprising unidirectional master-to-slave transmissionperiods and unidirectional slave-to-master transmission periods.
 8. Themethod according to claim 7, and comprising maintaining synchronizationon the given link, by: during the master-to-slave transmission periods,locking a local oscillator of the link-specific slave on thelink-specific clock signal of the link-specific master; and during theslave-to-master transmission periods, transmitting data from thelink-specific slave using the local oscillator that was locked on thelink-specific clock signal of the link-specific master during themaster-to-slave transmission periods.
 9. The method according to claim7, further comprising, in a processor, receiving the data from thecommunication devices over the Ethernet links, synchronizing the dataoriginating from the multiple sensors to a common time-base based onlink-specific clock-signal synchronization achieved on each of the linksby each link-specific master, and processing the synchronized data. 10.The method according to claim 9, wherein processing the synchronizeddata comprises constructing a three-dimensional image from the data thatoriginated from the multiple sensors, received over the multipleEthernet links and synchronized to the common time-base.
 11. The methodaccording to claim 9, wherein receiving the data in the processorcomprises receiving the data from at least two sensors over at least twoseparate Ethernet links.
 12. The method according to claim 9, whereinreceiving the data from the sensors comprises receiving images of ascene from image sensors, and wherein processing the synchronized datacomprises constructing a three-dimensional model of at least part of thescene from the images.